Abstract

Standing on a balcony near the top of the Tower of Pisa in Italy, a young scientist dropped two balls into the crowd below. The scientist, young Galileo, was not trying to knock his fellow professors on the head, but was trying to prove his theory that all objects fall to earth at the same rate, regardless of their mass. Was Galileo's theory correct? In this science project, you will get to test it out for yourself! Look out below!

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Introduction

Have you ever wondered how fast a heavy object falls compared to a lighter one? Imagine if you dropped both of them at the same time. Which would hit the ground first? In the 300s B.C.E. in Greece, the philosopher Aristotle was thinking about these same questions. He believed that heavier objects fall faster than lighter objects. For example, he thought that a ball that was 10 times as heavy as another ball would fall 10 times as fast. This means that if two objects are the same size, but one is heavier than the other, then when both objects are dropped from the same height and at the same time, the heavier object should hit the ground before the lighter object. But Aristotle did not actually test this idea. Was his theory right? Artistotle's idea makes intuitive sense to us because heavier objects feel heavier when we hold them. This has to do with the force of gravity. A force is something that pushes or pulls on something else. The weight we feel when we are holding an object is actually due to the downward force of Earth's gravity. Gravity is pulling the object down.

But gravity is not the only thing that affects how an object falls during free fall. Another factor is inertia (pronounced ih-nur-shuh). Inertia is the tendency of an object to stay in place, and not move. For example, imagine two carts, one stacked full of heavy books, and another that has some pillows on it. Which would you rather push, the cart with heavy books or the lighter cart? The cart with heavy books will be a lot harder to get moving. This is because the heavy cart has more inertia, which means that it takes more force to move the heavy cart. Can you imagine what inertia might have to do with falling objects? Figure 1, shows a ball falling over time. You know that the ball is pulled down because of gravity. However, when the ball is first dropped, it is moving more slowly because of inertia—the ball wanted to stay in place.

Figure 1. This image shows pictures of a ball that were taken as the ball was dropped. The pictures were taken at a constant rate so you can see how the speed of the ball changes over time. (Michael Maggs, 2007)

In the late 1500s C.E. in Italy, a young scientist and mathematician named Galileo Galilei questioned Aristotle's ideas about falling objects. He performed several experiments to test Aristotle's theories. As legend has it, in 1589 Galileo dropped two balls of different masses from a great height, near the top of the Tower of Pisa, to see which ball hit the ground first. What do you think he saw? While there is a lot of debate about whether this experiment actually took place, the story emphasizes the importance of using experimentation to test theories, even ones that have been around for nearly 2,000 years.

In this physics science project, you will do your own tests to determine whether heavier objects fall faster than lighter ones. Was Aristotle right, or did Galileo prove him wrong? How do you think gravity and inertia will affect your results? Get ready to test some ancient ideas and see how scientific history was made!

Terms and Concepts

Aristotle

Gravity

Force

Free fall

Inertia

Galileo

Mass

Questions

What force causes all objects to fall to the ground?

Where does this force come from?

What is inertia?

If an object has a lot of inertia, how does this affect how easy it is to move that object?

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Materials and Equipment

Balls of the same size, but different mass (2). For example, you could use a metal ball and a rubber or wooden ball that is about the same size. Or you could use two different balls used in sports that are the same size but have different weights.

Remember Your Display Board Supplies

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Experimental Procedure

If you are using a video camera to record your experiment, set the camera up now and have your helper get ready to record.

Climb the ladder or step stool with the two balls.

Drop the balls from the same height at the same time

If you are using a video camera, be sure to have your helper record the balls falling and hitting the ground. Also make sure to state for the camera each trial number.

Did one ball hit the ground before the other? Did they hit at the same time? In your lab notebook, make a data table like Table 1, and record your results in it by checking off which ball hit first.

If you recorded your trial, view the video recording to verify your results.

For any experiment, it is important to do multiple trials to assure that your results are consistent. Repeat the experiment (steps 1 to 4) at least 9 more times, making a total of at least 10 trials.

Be sure to always record your results in the data table in your lab notebook.

Trial #

Heavy Ball

Light Ball

Same Time

1

2

3

4

5

6

7

8

9

10

Total

Table 1. In your lab notebook, make a data table like this one to record your results in. Check off which ball hit the ground first, or if they hit the ground at the same time.

When you are done, add up the total number of trials that you got each result and write this in the "Total" row at the bottom of your data table.

Create a bar graph of your results.

You can make a graph by hand or use a website like Create a Graph to make a graph on the computer and print it.

Put the result ("Heavy Ball," "Light Ball," or "Same Time") on the x-axis (the horizontal axis going across) and the number of trials you got that result on the y-axis.

Look at your results. Did one of the balls usually hit the ground first, or did they usually land at the same time? Can you explain your results? Hint: If you are having trouble explaining your results, try re-reading the Introduction.

Communicating Your Results: Start Planning Your Display Board

Create an award-winning display board with tips and design ideas from the experts at ArtSkills.

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Variations

Try this experiment again, but this time use balls of the same mass, but different sizes. Does one ball hit the ground before the other, or do they hit it at the same time?

Try testing two objects that have the same mass, but are different shape. For example, you could try a large feather and a very small ball. Does one object hit the ground before the other, or do they hit it at the same time?

You could try other objects of different shapes, sizes, and masses. How do they fall compared to each other?

In this experiment you dropped balls through the air, but what happens when you drop them through something else, such as through water? You could try this experiment again but drop the balls in an aquarium filled only with water. Be sure that the balls you are using are safe to drop in the aquarium. Do you get the same results using water as you did using air, or are your results different somehow?

You could turn this physics science project into a human behavior science project by asking people which ball they think will hit the ground first, or if both balls will hit the ground at the same time. For an example of how to do this, watch this video on
Misconceptions About Falling Objects. You will probably need to re-read the information in the Introduction or do some more background research on inertia, gravity, speed (or velocity), and acceleration first to make sure you understand what result you should get, and why you should get this result. Do people usually give the right answer? If they have the right answer, can they explain it correctly?

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Ask an Expert

The Ask an Expert Forum is intended to be a place where students can go to find answers to science questions that they have been unable to find using other resources. If you have specific questions about your science fair project or science fair, our team of volunteer scientists can help. Our Experts won't do the work for you, but they will make suggestions, offer guidance, and help you troubleshoot.

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